This invention relates to a method an d a device for sampling material from a moving belt conveyor. The material to be sampled may be the run-of-mine product of mines such as metal mines in which the mineral to be recovered is unevenly distributed in the ore removed from the mining area.
The run-of-mine product may be considered to be the product reaching the first stage of ore processing after leaving the mining area. Typically, in an underground gold or platinum mine, the run-of-mine product arrives at the surface through a shaft, having been blasted and screened underground.
The ore in such mines contains mineral values which are not consistent from one working area of the mine to the others. There is also inconsistency in the distribution of the mineral in ore taken from the same working area. In underground gold mines, for instance, the ore may be concentrated in relatively narrow reefs or seams surrounded by barren country rock. Some country rock is always removed in such cases together with the metal-bearing reef or seam, and its presence necessarily affects the grade of the ore processed.
It is highly desirable to sample the run-of-mine product for its mineral values in order to establish the efficiency of the extraction process.
Because of the large tonnages typically handled in metal mines, and the disruption to production which would occur by periodically stopping a moving conveyor to remove a representative sample, run-of-mine sampling has not successfully been carried out on metal mines in the past, as far as the applicant is aware.
Fully representative sampling of bulk products is possible where the product is homogeneous. For instance, in the processing of food products such as maize and flour, it is possible to extract a satisfactory sample at almost any point. The sample in such cases need not be large: only sufficient product need be removed to satisfy the needs of the sapling procedure itself.
Typically in such instances a sample can be scooped off a moving or stationary conveyor such as a belt conveyor to provide a fully representative sample of the product at that point in the plant and at that particular time.
It has been appreciated that in order to conduct proper sampling of the run-of-mine product on metal mines, it is necessary to take a portion of the entire stream of material passing through a particular point at a particular time. The run-of-mine product in such mines is often transported, at least at some stage, on belt conveyors. Hitherto, to conduct run-of-mine sampling, the conveyor has been stopped, a former placed over a portion of the belt, and the entire body of ore contained within the former has been removed. The removal has, at least in some instances, taken place by laborious manual methods. These procedures have been slow and somewhat erratic since the consistency of operation of the person voiding the former cannot readily be sustained. Since a substantial proportion of the metal is often found in fines which settle at the bottom of a troughed belt conveyor, any significant part of the fines left behind can destroy the accuracy of the sampling result.
The problem is rendered more complicated by the fact that the ores are often highly abrasive so that there is a good deal of wear on any but the most robust of equipment.
The problem resolves itself largely into one of repeatability. It is necessary to be able to undertake a consistently repeatable procedure and one which does not disturb, to any real extent, the continuity of flow of the ore into the processing plant.
If the conveyor from which the sample is to be taken is a conventional belt conveyor the problem is compounded by the fact that belt geometry varies from point to point along the length of the conveyor. The belt, generally of rubber, is supported on a series of rollers, arranged in sets along the conveyor frame. Each set is arranged in a trough configuration. Between each pair of adjacent roller sets the belt tends to trough in a longitudinal direction in addition to the troughing imposed transversely by the rollers, so that a mechanism which merely travels in a straight line across the belt to eject a portion of the ore on it would not provide a sufficiently complete body of material to be adequate for proper sampling. The material contained in the trough, both longitudinal and transverse, would not be removed, and its presence would distort the results of the assaying procedure carried out on the sample extracted.
It is not however necessary that every particle of the body of material removed from the stream of ore should be collected. Provided the sampling procedure is entirely consistent and the extent of removal of the ore from the conveyor is understood, together with the overall distribution of metal in the ore, a satisfactory sampling result can be achieved by importing the necessary bias into the assay results.
With these and related circumstances in mind, it is an object of the invention to provide a method and apparatus for sampling material from a moving belt conveyor, such as the run-of-mine products of metal mines and similar mines, so that a successful and consistent result can be achieved.